STRONG: DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 177 
epidermis of the feather germ from the pulp. This was seen by 
Studer, but apparently overlooked by Davies. 
6. The cylinder-cell layer comprises cells having the characteristic 
cylindrical form, except in the region where there is an extensive 
growth of the intermediate cells which go to form the barbules. 
7. The initiative in the differentiation of ‘ ridges” is taken by the 
intermediate cells, uot by the cylinder-cell layer, nor by the dermis. 
8. The condition of asymmetry with reference to the rhachis in 
the vane of the completed feather is represented in a cross-section of the 
feather germ by an unequal number of ridges on the two sides of the 
rhachis, 7 
9. The ‘ Langsfurchen”’ described by Davies as occurring between 
successive ridges, and also within the ridges themselves, are artificial 
clefts due to imperfect fixation. 
10. The longitudinal extension of the feather germ is accomplished 
by proliferation of cells at its base and also by the growth of the cells 
composing the feather fundament. 
11. The columns of cells composing barbules experience bendings in 
two directions, resulting in a slightly spiral course. (1) By the growth 
of its component cells the barbule column increases greatly in length. 
Lateral extension in the feather germ being prevented by the confining 
sheath, its more distal portions are bent inwards until they come to 
lie nearly parallel with the long axis of the feather germ. (2) During 
the development of the feather the ridges become larger near their 
attachment to the rhachis. At a given level, as may be seen in cross- 
sections, this results in a crowding or lateral displacement of ridges 
towards the ventral side of the feather germ. The lateral plates (com- 
posed of barbule columns) are bent so that they present a concave face 
towards the rhachis, This condition is represented in a cross-section by 
the curving of the vows of barbule cells. ' 
12. While a deposit of melanin pigment in the more central of the 
medullary cells of the barb is usually associated with the production of 
blue, as described by Haecker, the pigment may occur in the barbules 
and not in the barbs. This is the case in the indigo bunting (Passerina 
cyanea). 
13. The melanins are supplied to the feather by branching pig- 
ment cells, which distribute their pigment rods to certain cells of the 
feather fundament during, or immediately preceding, early stages of 
cornification. 
14. The granules of melanin found in feathers are formed in the cyto- 
VOL. XL. — NO. 9. 3 
